The embodiments herein relate generally to a loudspeaker system and more specifically to an improved magnet configuration for generating enhanced sound.
The creation of robust hi-fidelity audio not only involves the science of carefully integrating an array of technologies for electronic to acoustic transformation, but also the art of passionately fine-tuning those integrated technologies within an optimized form factor to enrich the acoustic sound into an experience that is astounding to discerning audiophiles and inspiring to all. As such, modern loudspeakers have evolved over the years into truly enviable works of art and science. The invention described herein reflects the passion of combining art and science in a way that enhances the experience even more than what has been produced heretofore.
To appreciate the nuanced improvements described and claimed herein, it is first helpful to set the stage for those improvements by returning to the basics. In that regard, a loudspeaker is device that utilizes an electrical audio signal input to reciprocally drive controlled movement of ambient air to produce sound. The most common form of loudspeaker uses a paper cone supporting an electrical voice coil acting on a permanent magnet. In order to generate the wide range of frequencies necessary to reflect realistic sound, many speaker systems use multiple drivers each covering part of the range of frequencies desired from high to low levels. Ordinary listeners will recognize the driver names of subwoofers for very low frequencies, woofers for low frequencies, mid-range for middle frequencies, tweeters for high frequencies, and where desired, supertweeters for even higher frequencies.
Although different types of speaker drivers exist, one common type of driver employs a magnet surrounding an electrical voice coil to transform electrical input into a mechanical reciprocating motion of the voice coil that drives a diaphragm via a stiffly supported but lightweight carrier. As the voice coil carrier is driven in its reciprocating motion swiftly and repeatedly, the interconnected diaphragm moves with it, creating undulating sound waves perceived by the listeners as audio. The diaphragm is commonly recognized as the “cone” in a traditional mid-range or woofer speaker, or the “dome” of a tweeter design. The focus of the invention described and claimed herein is more on the driver system and less on the arrangement of the diaphragm and associated supports. Suffice it to say that a diaphragm is typically supported with primary and secondary support members that permit the desired reciprocating travel in response to signal input while dampening post-signal vibrations. The primary support member maintains the diaphragm in a centered and suspended position above the driver, while the secondary support centers and aligns the voice coil carrier that is connected to the diaphragm and serves to restore the voice coil and the diaphragm to a neutral position after moving. An inventive diaphragm arrangement is described in co-owned and co-pending application Ser. No. 13/283,529 filed on Oct. 27, 2011,the entire contents of which are incorporated herein by reference.
Regarding the driver system, a typical voice coil resides suspended within a cylindrical space or gap in a permanent magnet arrangement. When an electrical signal is applied to the voice coil, a magnetic field is created in the gap by the electric current in the voice coil, making it a variable electromagnet. Moreover, consideration of the appropriate materials for the components is important because of their impact on the distortion to the magnetic field and the impedance on the voice coil. In that regard, it may be helpful to refer to, among other publications, Bowler, J. R., A Theoretical Analysis of Eddy-Current Effects in Loudspeaker Motors, 48 J. Audio Eng. Soc., No. 7/8 (2000).
The electromagnetic field produced by the current through the coil is perpendicular to the permanent magnetic field in the air gap, generating a mechanical force that causes the voice coil (and thus the diaphragm) to reciprocate within the gap to create sound waves. The suspension system keeps the coil centered in the gap and provides a restoring (centering) force that returns the cone to a neutral position after moving. The permanent magnet is supported within a frame, sometimes referred to as a basket. The voice coil is oriented co-axially inside the gap; it moves back and forth within a small circular volume (a hole, slot, or groove) in the magnetic structure. The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside of the gap being one pole, and the center post, often called the pole piece, being the other. The pole piece and back plate are often manufactured as a single piece called a yoke.
The size and type of magnet and the particulars of the magnetic circuit may be different, depending on design goals. For instance, the shape of the pole piece affects the linearity of the magnetic field in the gap in which the voice coil operates. Likewise, different magnet structure geometries can improve the magnetic field stability dynamically when current is flowing through the coil. Often a shorting ring is employed to oppose fields induced by the coil. The benefits of a shorting ring include reduced impedance at high frequencies, providing extended treble output, reduced harmonic distortion, reduced inductance variation with voice coil movement, and a reduction in magnetic flux modulation that typically accompanies large voice coil excursions. To minimize modulation distortion of the magnetic field in the air gap, a shorting ring may be positioned below the permanent magnet.
Historically, permanent magnets that are configured in a cylindrical configuration have suffered from misaligned magnetic domains, reducing the effectiveness of the permanent magnet to impact reciprocating movement of the voice coil. It has been determined that manufacturing the permanent magnet into discrete, sintered, arcuate components, that are configured to be joined end-to-end into a cylinder, permits a greater alignment of magnetic domains and enhances effectiveness. Each arcuate component, or arc, is conventionally coated with a conductive coating, such as nickel, to reduce corrosion of the underlying magnet material. Although the result is beneficial to durability, the nickel tends to generate an undesired eddy-current.
The present invention comprises embodiments that overcome some of the limitations of the prior art systems, each of which may achieve some or all of the benefits afforded by the present invention.